Biodegradation of atrazine in surface soils and subsurface sediments collected from an agricultural research farm

Abstract

The purpose of the present study was to assess atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) mineralization by indigenous microbial communities and to investigate constraints associated with atrazine biodegradation in environmental samples collected from surface soil and subsurface zones at an agricultural site in Ohio. Atrazine mineralization in soil and sediment samples was monitored as 14CO2 evolution in biometers which were amended with 14C-labeled atrazine. Variables of interest were the position of the label ([U-14C-ring]-atrazine and [2-14C-ethyl]-atrazine), incubation temperature (25 degrees C and 10 degrees C), inoculation with a previously characterized atrazine-mineralizing bacterial isolate (M91-3), and the effect of sterilization prior to inoculation. In uninoculated biometers, mineralization rate constants declined with increasing sample depth. First-order mineralization rate constants were somewhat lower for [2-14C-ethyl]-atrazine when compared to those of [U-14C-ring]-atrazine. Moreover, the total amount of 14CO2 released was less with [2-14C-ethyl]-atrazine. Mineralization at 10 degrees C was slow and linear. In inoculated biometers, less 14CO2 was released in [2-14C-ethyl]-atrazine experiments as compared with [U-14C-ring]-atrazine probably as a result of assimilatory incorporation of 14C into biomass. The mineralization rate constants (k) and overall extents of mineralization (Pmax) were higher in biometers that were not sterilized prior to inoculation, suggesting that the native microbial populations in the sediments were contributing to the overall release of 14CO2 from [U-14C-ring]-atrazine and [2-14C-ethyl]-atrazine. A positive correlation between k and aqueous phase atrazine concentrations (Ceq) in the biometers was observed at 25 degrees C, suggesting that sorption of atrazine influenced mineralization rates. The sorption effect on atrazine mineralization was greatly diminished at 10 degrees C. It was concluded that sorption can limit biodegradation rates of weakly-sorbing solutes at high solid-to-solution ratios and at ambient surface temperatures if an active degrading population is present. Under vadose zone and subsurface aquifer conditions, however, low temperatures and the lack of degrading organisms are likely to be primary factors limiting the biodegradation of atrazine.

Kinetics of aerobic and anaerobic biomineralization of atrazine in surface and subsurface agricultural soils in Ohio

“…Hydrophobic partitioning into soil organic matter is also an important mechanism of atrazine retention in soils. [25][26][27][28] The log K ow value for atrazine is 2.5, clear indication for its sorption into soil organic matter as previously demonstrated by Radosevich et al [3,29] While the attenuation of atrazine by microorganisms in surface and subsurface soils has been demonstrated in numerous publications, [1][2][3][4][5][6][7][8] the biomineralization of atrazine in subsurface as a function of soil depth is not well documented. The objective of this study was to measure aerobic and anaerobic mineralization of atrazine in vertical core samples retrieved from two agricultural sites.…”

“…[1][2][3][4][5][6][7] Biodegradation occurs under bulk aerobic conditions in soil surface layers as well as in the underlying zones that are increasingly microaerophilic with depth and ultimately anoxic. Anoxic microsites also exist in soil aggregates in surface layers.…”

Molecular analysis of atrazine-degrading bacteria and catabolic genes in the water column and sediment of a created wetland in an agricultural/urban watershed

“…The mineralization of atrazine was tested in aerobic 60 ml biometer bottles fitted with rubber septa, as previously described (Radosevich et al, 1996). The biometers were inoculated with 6-10 diced Bio-Sep beads.…”

Effects of Atrazine-Mineralizing Microorganisms on Weed Growth in Atrazine-Treated Soils

“…Accelerated atrazine degradation in soil has been found in the laboratory only and under certain conditions (Radosevich et al, 1996;Vanderheyden et al, 1997). Numerous research groups tried for many years to enrich microorganisms capable of mineralizing this chemical as a carbon and energy source (Cook, 1987) until Yanze Kontchou and Gschwind (1994) and Radosevich et al (1995) independently succeeded in isolating atrazine-degrading bacteria.…”